Ch. 2 Genetics Homework

Front 1

In an organism with 52 chromosomes, how many bivalents would be expected to form during meiosis?

Back 1

26

Front 2

In a healthy male, how many sperm cells would be expected to be formed from a) 400 primary spermatocytes, b) 400 secondary spermatocytes?

Back 2

a) 1600 b) 800

Front 3

In a healthy female, how many secondary oocytes and first polar bodies would be expected to form from 100 primary oocytes?

Back 3

100,100

Front 4

If the G1 somatic cell nucleus in a female insect contains 2 picograms of DNA, how much DNA would be expected in the metaphase I cycle of the same cell?

Back 4

4 picograms**

Front 5

What is the outcome of synapsis?

Back 5

side-by-side alignment of homologous chromosomes

Front 6

Which of the following occur in meiosis but NOT in mitosis?
I. Separation of sister chromatids on microtubules
II. Pairing of homologous chromosomes
III. Recombination between sister chromatids

Back 6

II only *

Front 7

If cells are blocked in meiotic metaphase II and prevented from moving on in meiosis, which one of the following will be prevented?

Back 7

separation of sister chromatids

Front 8

During interphase of the cell cycle

Back 8

DNA content essentially doubles

Front 9

A gamete normally contains how many copies of each chromosome?

Back 9

1

Front 10

How many haploid sets of chromosomes are present in an individual cell that is tetraploid (4n)?

Back 10

4

Front 11

1) A chromosome may contain one or two chromatids in different phases of the mitotic or meiotic cell cycle. T / F

Back 11

True

Front 12

2) If a typical G1 nucleus is 2n and contains two complements (2C) of DNA, a prophase I cell is 2n and contains 4C DNA. T / F

Back 12

True

Front 13

3) During meiosis chromosome number reduction takes place in anaphase II. T / F

Back 13

False, telophase 1

Front 14

4) The centromere of a chromosome separates during anaphase. T / F

Back 14

True

Front 15

5) The meiotic cell cycle involves two cell divisions and two DNA replications. T / F

Back 15

False 1 DNA replication

Front 16

Discuss the concepts of homologous chromosomes, haploidy and diploidy. What characteristics do two homologous chromosomes share?

Back 16

Homologous chromosomes- are two chromosomes paired up in a set of chromosomes.
- have identical gene locus
- identical overall length
- same position of centromere
- banding patterns
- autoradiographic pattern

haploidy: only one set of chromosomes; only one of the homologous chromosomes after meiotic division.
diploidy: two sets of chromosomes; has both homologous chromosomes

Front 17

If two homologous chromosomes of chromosome # 12 fail to separate during meiosis I, how many copies of chromosome # 12 will the resulting gametes have?

Back 17

Two will have double (2), and two will have zero.

Front 18

In what way does the second division of meiosis differ from mitosis?

Back 18

mitosis: sister chromatids are identical
meiosis: recombination; sister chromatids are different.
Recombination swaps DNA between sister and non sister chromatids.

Front 19

If children obtain half their genes from one parent and half from the other parent, why aren’t siblings identical?

Back 19

There are differnet formas of genetic variation.
- recombination -crossing over
- independent assotrment
These together can produce a combinatorial explosion of possibilities of the genetic makeup of offspring.

Front 20

Human cells normally have 46 chromosomes. For each of the following stages, state the number of chromatids (or chromosomes) present in a human cell.

a) Metaphase of mitosis
b) Metaphase I of meiosis
c) Telophase of mitosis
d) Telophase I of meiosis
e) Telophase II of meiosis

Back 20

a) 92 chromatids
b) 92 Chromatids
c) 92
d) 46 Chromatids
e) 46 Chromatids

Front 21

6) In a diploid organism of 2n=10, assume that you can label all the centromeres derived from both female and male parent. When this organism produces gametes, how many male- and female- labeled centromere combinations are possible in the gametes?

Back 21

32

Front 22

7) a) Contrast spermatogenesis and oogenesis.
b) What is the significance of the formation of polar bodies?

Back 22

Spermatogenesis: primary spermatocyte makes two secondary spermatocyte and each of those make two sperm.

Oogenesis- primary oocyte & primary polar body make primary oocyte and an ovum.
The polar bodies are there because there must be two bodies made, but this allows the ovum to have all of the cytoplasm and nutrients necessary to provide for a zygote.

Front 23

8) Regarding the mitotic cell cycle, what is meant by a check-point? What are the different checkpoints and how do they serve us?

Back 23

Checkpoints are pauses in teh cell cylce to make sure that there are no errors made in any replication, etc. They make sure all things are correct.

Front 24

9) Trisomy 21 or Down syndrome occurs when there is a normal diploid chromosomal complement of 46 chromosomes plus one extra chromosome # 21 (total 47 chromosomes). Assume that a mating happens between a Down syndrome female and a normal male (46 chromosomes). What proportion of offspring will be expected to have Down syndrome? Explain.

Back 24

One-half of the offspring will be expected to have Down syndrome because of 2*1 segregation of chromosome # 21 at anaphase I.

Front 25

Q 10

Back 25

in book

Front 26

11) In a diploid organism with a chromosome no of 46 (2n = 46), and G1 nuclear DNA content of 13 picograms;

a) What is the haploid number?
b) During metaphase of mitosis how many chromatids are present in each somatic cell?
c) How many haploid sets of chromosomes are present in each cell?
d) What is the nuclear DNA content of the G2 cell?

Back 26

23, 92, 2, 26 (13X2)

Front 27

12) A species of wheat has a chromosome number of 30, while a species of rye has a chromosome number of 14. Sterile hybrids can be produced by crossing these two plants.

a) What would be the expected chromosome number in the somatic cells of the hybrids?
b) The G1 nuclear DNA content of wheat is 5.5 picograms, and that of rye is 16.8 picograms. What would be the expected DNA content in a metaphase somatic cell of the hybrid?

Back 27

22, 22.3

Front 28

1) A recessive allele in tigers causes the white tiger. If two normally pigmented tigers are mated and produce a white offspring, what percentage of their remaining offspring would be expected to have normal pigmentation?

Back 28

75%

Front 29

2) Polydactyly is expressed when an individual has extra fingers/ toes. Having extra digits is caused by a dominant allele. If a man with polydactyly marries a woman with normal number of digits and has one son with normal hands and feet and one with extra digits; what is the probability that their next child will have polydactyly?

Back 29

1/2

Front 30

3) Tightly curled hair is caused by a dominant gene in humans. If a heterozygous curly-haired person marries a person with straight hair; what fraction of their offspring would be expected to have straight hair?

Back 30

1/2 straight

Front 31

4) What type of genotypic and phenotypic ratios are likely to occur in crosses when dealing with a single gene pair where all the genotypic combinations are of equal viability?

Back 31

1:2:1, 3:1

Front 32

5) Assume that a black guinea pig crossed with an albino guinea pig produced five black offspring. When the albino was crossed with a second black one, 4 black and 3 albino offspring were produced. What genetic explanation would apply to these data?

Back 32

albino = recessive, black = dominant

Front 33

6) The fundamental Mendelian process that involves the separation of contrasting genetic elements at the same locus would be called

Back 33

segregation

Front 34

he Chi-square test involves a statistical comparison between observed and expected values. One generally determines degrees of freedom as

Back 34

one less the number of classes being compared.

Front 35

1) Mendel’s law of segregation is supported by a 1:1 testcross ratio. T/F

Back 35

True

Front 36

2) The non-functional form of a gene is called a wild-type allele.

Back 36

False

Front 37

3) A gene can have maximum two alleles

Back 37

False

Front 38

4) To test Mendel’s Law of Independent Assortment, the experimenter needs a minimum of two different genes and their two alleles.

Back 38

True

Front 39

5) A 1:1 phenotypic ratio is expected from a monohybrid testcross with complete dominance.

Back 39

True

Front 40

1) What phenotypic ratios are likely to occur in crosses when dealing with two completely dominant, independently segregating gene pairs, when both parents are heterozygous?

Back 40

9:3:3:1

Front 41

2) Provide simple definitions that distinguish segregation and independent assortment

Back 41

segregation- separation of alleles during meiosis

independent assortment- one gene pair has an equal and independent opportunity of segregating with either member of another gene pair.

Front 42

3) In Chi-square analysis, what condition causes one to reject the null-hypothesis?

Back 42

a p-value smaller than .05

Front 43

4) Assuming a typical monohybrid cross in which one allele is completely dominant to the other, what ratio is expected if the F1’s are crossed?

Back 43

3:1

Front 44

5) Under what conditions does one expect a 1:1:1:1 ratio?

Back 44

double heterozygotes crossed with fully recessive individuals

Front 45

6) Assume that a Ch-square test provided a probability value of 0.02. Should the null hypothesis be accepted?

Back 45

no